How secure is the "Captains Log"?

I was thinking about how In The Pale Moonlight if anyone had been tapping Sisko's private logs the entire Romulan scheme would have fallen apart. I know he deletes the log at the end but I don't think that would have done much for anyone listening in.

The logs are transmitted as communications back to Starfleet HQ right? So it's not completely on some internal system.